Sahara

Satellite image

The Sahara is the world's largest hot desert, over 9,000,000 km² (3,500,000 mi²), almost as large as the United States. The Sahara is located in northern Africa and is 2.5 million years old. Its name, Sahara, is an English pronunciation of the word for desert in Arabic (صحراء ).

Overview

The top image shows the Safsaf Oasis on the surface of the Sahara. The bottom (using radar) is the rock layer underneath, revealing black channels cut by the meandering of an ancient river that once fed the oasis.

The boundaries of the Sahara are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean Sea on the north, the Red Sea and Egypt on the east, and the Sudan and the valley of the Niger River on the south. The Sahara is divided into western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains (a region of desert mountains and high plateaus), Tenere desert and the Libyan desert (the most arid region). The highest peak in the Sahara is Emi Koussi (3415 m) in the Tibesti Mountains in northern Chad.

The Sahara divides the continent of Africa into North and Sub-Saharan Africa. The southern border of the Sahara is marked by a band of semiarid savanna called the Sahel; south of the Sahel lies the lusher Sudan and the Congo River Basin. Most of Sahara consists of rocky hamada, Ergs (large sand dunes) form only minor part.

Humans have lived on the edge of the desert for almost 500,000 years. Imediately after the last ice age, the Sahara was a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles survive in total with half found in the Tassili n'Ajjer in southeast Algeria. Fossils of dinosaurs, like Afrovenator, Jobaria and Ouranosaurus, have also been found here. The modern Sahara, though, is not as lush in vegetation, except in the Nile Valley, at a few oases, and in the northern highlands, where Mediterranean plants such as the olive tree grow. It has been this way since about 3000 BCE.

2.5 million people live in the Sahara, most of these in Egypt, Mauritania, Morocco and Algeria. Dominant ethnicities in the Sahara are various Berber groups including Tuareg tribes, various Arabised Berber groups such as the Hassaniya speaking Maure/Moors (also known as Sahrawis) and various "black African" ethnicities including Tubu, Nubians, Zaghawa,Kanuri, Peul (Fulani), Hausa and Songhai. The largest city in the Sahara is Cairo, in the Nile Valley and Egypt's capital. Other important cities are Nouakchott, the capital of Mauritania; Tamanrasset, Algeria; Timbuktu, Mali; Agadez, Niger; Ghat, Libya; and Faya, Chad.

Climate History

The climate of the Sahara has undergone enormous variation between wet and dry over the last few hundred thousand years. During the last ice age, the Sahara was bigger than it is today, extending south beyond its current boundariesChristopher Ehret. The Civilizations of Africa. University Press of Virginia, 2002.. The end of the ice age brought wetter times to the Sahara, from about 8000 BCE to 6000 BCE, perhaps due to low pressure areas over the collapsing ice sheets to the northFezzan Project - Palaeoclimate and environment.

Once the ice sheets were gone, the northern part of the Sahara dried out. However, not long after the end of the ice sheets, the monsoon which currently brings rain to the Sahel came further north and counteracted the drying trend in the southern Sahara. The monsoon in Africa (and elsewhere) is due to heating during the summer. Air over land becomes warmer and rises, pulling cool wet air in from the ocean. This causes rain. So, paradoxically, the Sahara was wetter when it received more insolation in the summer. In turn, changes in solar insolation are caused by changes in the Earth's orbital parameters.

By around 2500 BCE, the monsoon retreated south to approximately where it is todaySahara's Abrupt Desertification Started By Changes In Earth's Orbit, Accelerated By Atmospheric And Vegetation Feedbacks, leading to the desertification of the Sahara. The Sahara is currently as dry as it was about 13,000 years ago.White, Kevin and Mattingly, David J. 2006. Ancient Lakes of the Sahara. American Scientist. Volume 94 Number 1 (January-February, 2006). pp. 58-65.

History

The sun shines over Saharan dunes.

Cattle Period

By 6000 BCE predynastic Egyptians in the southwestern corner of Egypt were herding cattle and constructing large buildings. Subsistence in organized and permanent settlements in predynastic Egypt by the middle of the 6th millennium BCE centered predominantly on cereal and animal agriculture: cattle, goats, pigs and sheep.Predynastic (5,500 - 3,100 BC) www.touregypt.net Metal objects replaced prior ones of stone. Tanning animal skins, pottery and weaving are commonplace in this era also. There are indications of seasonal or only temporary occupation of the Al Fayyum in the 6th millennium BCE, with food activities centering on fishing, hunting and food-gathering.Fayum, Qarunian (Fayum B) (about 6000-5000 BC?) www.digitalegypt.ucl.ac.uk Stone arrowheads, knives and scrapers are common. Burial items include pottery, jewelry, farming and hunting equipment, and assorted foods including dried meat and fruit. The dead are buried facing due west.

Berber Period

The Phoenicians created a confederation of kingdoms across the entire Sahara to Egypt, generally settling on the coasts but sometimes in the desert also.

By 2500 BC the Sahara was as dry as it is today and it became a largely impenetrable barrier to humans, with only scattered settlements around the oases, but little trade or commerce through the desert. The one major exception was the Nile Valley. The Nile, however, was impassable at several cataracts making trade and contact difficult.

Sometime between 633 and 530 BCE Hanno the Navigator either established or reinforced Phoenician colonies in the Western Sahara, but all ancient remains have vanished with virtually no trace. See History of Western Sahara.

Greeks

By 500 BCE a new influence arrived in the form of the Greeks and Phoenicians. Greek traders spread along the eastern coast of the desert, establishing trading colonies along the Red Sea coast. The Carthaginians explored the Atlantic coast of the desert. The turbulence of the waters and the lack of markets never led to an extensive presence further south than modern Morocco. Centralized states thus surrounded the desert on the north and east; it remained outside of the control of these states. Raids from the nomadic Berber people of the desert were a constant concern of those living on the edge of the desert.

Urban civilizaion

An urban civilization, the Garamantes, arose around this time in the heart of the Sahara, in a valley that is now called the Wadi al-Ajal in Fazzan, in Libya. The Garamantes achieved this development by digging tunnels far into the mountains flanking the valley to tap fossil water and bring it to their fields. The Garamantes grew populous and strong, conquering their neighbors and capturing many slaves (which were put to work extending the tunnels). The ancient Greeks and the Romans knew of the Garamantes and regarded them as uncivilized nomads. However, they traded with the Garamantes, and a Roman bath has been found in the Garamantes capital of Garama. Archaeologists have found eight major towns and many other important settlements in the Garamantes territory. The Gartamantes civilization eventually collapsed after they had depleted available water in the aquifers, and could no longer sustain the effort to extend the tunnels still further into the mountains.Keys, David. 2004. Kingdom of the Sands. Archaeology. Volume 57 Number 2, (March/April 2004)Abstract - retrieved March 13 2006

Arab invasion

The greatest change in the history of the Sahara arrived with the Arab invasion that brought camels to the region. For the first time an efficient trade across the Sahara desert could be conducted. The kingdoms of the Sahel, especially the Ghana Empire and the later Mali Empire, grew rich and powerful exporting gold and salt to North Africa. The emirates along the Mediterranean sent south manufactured goods and horses. From the Sahara itself salt was exported. This process turned the scattered oasis communities into trading centres, and brought them under the control of the empires on the edge of the desert.

This trade persisted for several centuries until the development in Europe of the caravel allowed ships, first from Portugal but soon from all Western Europe, to sail around the desert and gather the resources from the source in Guinea. The Sahara was rapidly remarginalized.

The colonial powers also largely ignored the region, but the modern era has seen a number of mines and communities develop to exploit the desert's natural resources. These include large deposits of oil and natural gas in Algeria and Libya and large deposits of phosphates in Morocco and Western Sahara.

mtDNA analyses Z. Brakez et al., "Human mitochondrial DNA sequence variation in the Moroccan population of the Souss area" extract www.ncbi.nlm.nih.gov found that various populations have contributed to the present-day gene pool of the Souss region of southern Morocco, including Berbers, Arabs, Phoenicians, Sephardic Jews, and sub-Saharan Africans. Throughout the Sahara, Berbers, Arabs, and sub-Saharan Africans are significantly represented genetically.

References

*Pigs in Ancient Egypt by Marie Parsons www.touregypt.net
*Michael Brett and Elizabeth Frentess. The Berbers. Blackwell Publishers. 1996.
*Charles-Andre Julien. History of North Africa: From the Arab Conquest to 1830. Praeger, 1970.
*Abdallah Laroui. The History of the Maghrib: An Interpretive Essay. Princeton, 1977.
*Hugh Kennedy. Muslim Spain and Portugal: A Political History of al-Andalus. Longman, 1996.
*Fezzan Project - Palaeoclimate and environment - retrieved March 15 2006

External links

*Trans-Sahara routes
*Interactive Google Satellite image of the Sahara (Northern Africa)
*Sahara pictures from Algerian UN Permanent Mission website
*Over 3000 pictures of the Sahara
*Flora and Fauna of the Sahara

Sahara: Encyclopedia BETA

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